Car power source apparatus

ABSTRACT

The car power source apparatus is provided with contactors  2  connected to the output-side of the battery  1;  a pre-charge circuit  3  made up of a series connected pre-charge resistor  6  and a pre-charge relay  7,  which is connected with a contactor  2  to supply auxiliary charge to a capacitor  21  connected to the car-side of the battery  1;  and a control circuit  4  to control the contactors  2  and pre-charge relay  7. The pre-charge resistor  6  is connected in parallel with a contactor  2,  and the pre-charge relay  7  is connected in series with that contactor  2.  The control circuit  4  switches the pre-charge relay  7  ON to pre-charge the car-side capacitor  21,  and then switches the contactor  2  ON to connect the battery  1  to the car-side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power source apparatus that connectsthe vehicle driving battery to the car-side load via contactors (highpower, electric automotive-grade relays), and in particular relates to acar power source apparatus that prevents the detrimental effects offused contacts.

2. Description of the Related Art

The car power source apparatus has first and second contactors thatconnect to the positive and negative output-side of the battery. In thispower source apparatus, contactors are switched ON to connect thebattery with the car-side load. When the vehicle is not in use, forexample, when the automobile ignition switch is OFF, the contactors areswitched OFF. Furthermore, if the automobile has an accident orcollision, the contactors are also switched OFF to cut-off batteryoutput and increase safety.

A capacitor with a large capacitance value is connected in parallel withthe car-side load that connects with the power source apparatus. Itspurpose is to instantaneously output high power. The capacitor ischarged by the battery. Since the capacitance of the capacitor is high,charging current becomes extremely large when the capacitor iscompletely discharged. Consequently, when the contactors, which connectto the positive and negative output-side of the battery, are switchedON, extremely large transient charging current can flow. Large chargingcurrent can damage contacts on the contactors. In particular, contactorcontacts can fuse together due to large charging current. If thecontacts fuse together, the contactors cannot be switched OFF and thedriving battery cannot be disconnected from the load. To prevent thisnegative result, a power source apparatus has been developed that isprovided with a pre-charge circuit to pre-charge the capacitor beforeturning the contactors ON (refer to Japanese Patent ApplicationDisclosure 2005-295697).

As shown in FIG. 1, the car power source apparatus cited in disclosure2005-295697 is provided with a pre-charge circuit to supply auxiliarycharge to the capacitor. The pre-charge circuit is connected in parallelwith the first contactor on the positive-side of the battery andsupplies auxiliary charge to the capacitor while limiting current. Thispre-charge circuit is provided with a current-limiting pre-chargeresistor, and a pre-charge relay connected in series with the pre-chargeresistor. In this power source apparatus, the second contactor connectedto the negative-side of the battery and the pre-charge relay areswitched ON to pre-charge the capacitor. After the capacitor ispre-charged, the first contactor is switched ON to connect the batterywith the car-side.

In the power source apparatus shown in FIG. 1, if the car-side becomesshort circuited, extremely high current, for example 1000A of shortcircuit current, can flow through the contactors. High short circuitcurrent is a cause of contactor contacts fusing together. In particular,if the contacts “chatter” under short circuit conditions, they caneasily become fused together. Contactors are switched ON and OFF eachtime the car ignition switch is turned ON and OFF. Further, since thecontactors switch high currents, a long-lifetime durable metal such astungsten is used as the contact material. For example, currently adoptedcontactors utilize durable contacts having fixed contacts of copper, andmoveable contacts of tungsten laminated on a copper surface. Durablecontacts demonstrate superior long-lifetime characteristics whenswitched ON and OFF with high currents. However, contactors providedwith durable contacts cannot effectively prevent fused contacts due tohigh current flow from a car-side short circuit. This is because ifcontact “chatter” occurs under high current conditions, tungsten, whichis a durable contact material, will be heated to high temperature andmelt copper.

Fused contacts due to short circuit current can be prevented withhigh-capacity type contacts having fixed contacts and moveable contactsmade of copper. However, while high-capacity type contacts made ofcopper can prevent short circuit induced fused contacts, they have thedrawback that long-lifetime cannot be achieved. Copper, which is ahigh-capacity type contact material, shows low contact temperature risedue to short circuit current flow, but it has a low melting point.Tungsten, which is a durable contact material, shows high contacttemperature rise due to short circuit current flow, but it has a highmelting point. Consequently, in a contactor having fixed contacts ofcopper and moveable contacts with tungsten on the surface, the tungstenwill be heated to high temperature by short circuit current and copperwill melt causing the contacts to fuse together. Contactors with fixedand moveable contacts of copper show less contact temperature rise dueto short circuit current and can better prevent fused contacts thancontactors with tungsten contacts, but they cannot achievelong-lifetime. Therefore, to implement long contact lifetime, prior artcar power source apparatus have the drawback that fused contacts due tocar-side short circuit cannot be prevented. If contactor contacts becomefused together, battery output cannot be cut-off and it is difficult toinsure safety. A car power source apparatus that can reliably switch OFFcontactors to cut-off battery output under abnormal conditions is indemand. While prior art power source apparatus contactors can achievelong-lifetime, prevention of short circuit current induced fusedcontacts is extremely difficult. Prior art power source apparatuscontactors have the drawback that long-lifetime and prevention of fusedcontacts are mutually exclusive characteristics that cannot both besatisfactorily realized.

The present invention was developed to further resolve these drawbacks.Thus, it is a primary object of the present invention to provide a carpower source apparatus that can reliably cut-off battery output inabnormal circumstances while achieving long contactor lifetime.

SUMMARY OF THE INVENTION

The car power source apparatus of the present invention is provided witha battery 1; contactors 2 connected to the output-side of the battery 1;a pre-charge circuit 3 made up of a series connected pre-charge resistor6 and a pre-charge relay 7 in turn connected with a contactor 2 tosupply auxiliary charge to a capacitor 21 connected to the car-side ofthe battery 1; and a control circuit 4 to control the contactors 2 andpre-charge relay 7. Further, the pre-charge resistor 6 is connected inparallel with a contactor 2, and the pre-charge relay 7 is connected inseries with that contactor 2. In this power source apparatus, thecontrol circuit 4 switches the pre-charge relay 7 ON to pre-charge thecar-side capacitor 21, and then switches the contactor 2 ON to connectthe battery 1 to the car-side.

A car power source apparatus having the configuration described aboverealizes the characteristic that battery output can be reliably cut-offin abnormal circumstances while achieving long contactor lifetime. Thisis because the pre-charge resistor is connected in parallel with acontactor and the pre-charge relay is connected in series with thatcontactor. In a power source apparatus of this configuration, thecontactor connected in series with the pre-charge relay is maintainedOFF, and the pre-charge relay is turned ON to pre-charge the car-sidecapacitor. Subsequently, the pre-charge relay is maintained ON, and thecontactor connected in series with the pre-charge relay is switched ONto connect the battery to the car-side. In this state, battery output isconnected to the car-side via the pre-charge relay and the contactors.If a car-side short circuit occurs and contacts fuse together, as longas the contacts of both the pre-charge relay and the series connectedcontactor do not fuse together, battery output can be cut-off in anabnormal situation. Contact fusing for a series connection of contactorand pre-charge relay can be less likely. This is because energyresulting from short circuit current flow is distributed among, anddissipated by the contacts of the contactor and the pre-charge relay.For example, if the contacts of both the contactor and pre-charge relayare “chattering,” energy consumption is distributed between both sets ofcontacts and contact fusing is less likely. Even if contact fusingoccurs under these conditions, the probability of contacts fusingtogether in both the contactor and pre-charge relay is low. Therefore,battery output can be cut-off by the contacts that do not fuse together.If one set of contacts for the contactor and pre-charge relay retaintheir ON state without “chattering” under short circuit currentconditions while the other set of contacts “chatters,” the contacts withno “chatter” will not fuse together even if the “chattering” contactsfuse.

Contactors 2 in the power source apparatus can be provided with a firstcontactor 2A and a second contactor 2B connected to the positive andnegative output-side of the battery 1. In this power source apparatus,the pre-charge resistor 6 is connected in parallel with the firstcontactor 2A, and the first contactor 2A and the pre-charge relay 7 areconnected in series. In this power source apparatus, the first contactor2A and the second contactor 2B can be switched OFF to cut-off positiveand negative battery output. In addition, even if either contactorbecomes fused together, battery output can be cut-off.

The contactor 2 connected in series with the pre-charge relay 7 can beprovided with longer lifetime contacts than those of the pre-chargerelay 7, and the pre-charge relay 7 can be provided with higher capacitycontacts than those of the contactor 2 connected in series with thepre-charge relay 7. In this power source apparatus, contacts of thepre-charge relay, which are high-capacity type contacts, are difficultto fuse together with short circuit current, and battery output can becut-off in abnormal circumstances by switching the pre-charge relay OFF.Further, since the contactor connected in series with the pre-chargerelay uses long-lifetime contacts, contact lifetime for both thecontactor and the pre-charge relay can be extended by switching theseries connected contactor OFF prior to switching the pre-charge relayOFF. Consequently, contact lifetime can be extended while allowingreliable cut-off of battery output in abnormal circumstances.

Contacts of the contactor 2 connected in series with the pre-chargerelay 7 can be long-lifetime contacts having tungsten at least on thesurface. Specifically, contacts of the contactor 2 connected in serieswith the pre-charge relay 7 can be long-lifetime contacts with tungstenlayered on a copper surface. Further, for the contactor 2 connected inseries with the pre-charge relay 7, contacts on one side can be copper,and those on the other side that mate with the copper contacts can belong-lifetime contacts having a tungsten surface. Tungsten contacts canbe repeatedly cycled ON and OFF with little damage allowing extendedlifetime for the contactor connected in series with the pre-chargerelay.

Contacts of the pre-charge relay 7 can be high-capacity type contactsmade of copper. In this power source apparatus, short circuit inducedfused contacts can be prevented while reducing voltage drop across thepre-charge relay. This is because the copper used in the contacts haslow electrical resistance and high specific heat.

Contacts of the second contactor 2B can be higher capacity type contactscompared to those of the first contactor 2A. Further, contacts of thesecond contactor 2B can be copper high-capacity type contacts. In thispower source apparatus, fusing together of the contacts of the secondcontactor due to short circuit current can be prevented, and batteryoutput can be reliably cut-off in abnormal circumstances.

Further, the delay time for switching OFF the pre-charge relay 7 afterswitching OFF the contactor 2 connected in series with the pre-chargerelay 7 can be stored in memory by the control circuit 4. In this powersource apparatus, the time after switching OFF the contactor 2 connectedin series with the pre-charge relay 7 is detected to switch OFF thepre-charge relay 7. This power source apparatus can extend contactlifetime for the pre-charge relay. In particular, pre-charge relaycontact lifetime can be extended while using high-capacity typecontacts. This is because full battery current is shut-off when thepre-charge relay contacts are switched OFF.

The above and further objects of the present invention as well as thefeatures thereof will become more apparent from the following detaileddescription to be made in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art car power source apparatus;

FIG. 2 is a block diagram of an embodiment of the car power sourceapparatus of the present invention;

FIG. 3 is a block diagram of another embodiment of the car power sourceapparatus of the present invention;

FIG. 4 is an abbreviated diagram of a relay used as the first contactorshown in FIG. 2; and

FIG. 5 is an abbreviated diagram of a relay used as the pre-charge relayand the second contactor shown in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The car power source apparatus shown in FIG. 2 is installed in a hybridcar or electric automobile, and is connected to an electric motor 22 asits load 20 to drive the vehicle. The power source apparatus of thefigure is provided with a driving battery 1; first and second contactors2 connected to the output-side of the battery 1; a pre-charge circuit 3to pre-charge the load 20 capacitor 21 prior to switching the firstcontactor 2A ON; and a control circuit 4 to control the pre-chargecircuit 3, the first contactor 2A, and the second contactor 2B ON andOFF.

As shown in FIG. 3, the power source apparatus of the present inventioncan have a circuit configuration with a pre-charge circuit 3 andcontactor 2 connected only at the positive-side of the battery 1, andwith no contactor 2 connected at the negative-side of the battery 1. Inaddition, although not illustrated, a circuit configuration with apre-charge circuit 3 and contactor 2 connected only at the negative-sideof the battery 1, and with no contactor 2 connected at the positive-sideof the battery 1, is also possible.

In the power source apparatus of FIG. 2, the first contactor 2A, whichhas the pre-charge circuit 3 connected, is connected to thepositive-side of the battery 1, and the second contactor 2B, which doesnot have the pre-charge circuit 3 connected, is connected to thenegative-side of the battery 1. However, although not illustrated, thepower source apparatus of the present invention can also be configuredwith the first contactor 2A, which has the pre-charge circuit 3connected, connected to the negative-side of the battery 1, and thesecond contactor 2B, which does not have the pre-charge circuit 3connected, connected to the positive-side of the battery 1. Thefollowing describes in detail a power source apparatus with the circuitstructure of FIG. 2.

A capacitor 21 with large capacitance is connected in parallel with theload 20. With the contactors 2 in the ON state, electric power issupplied to the load 20 from both the capacitor 21 and the battery 1. Inparticular, instantaneous high power is supplied to the load 20 from thecapacitor 21. For this reason, the instantaneous power that can besupplied to the load 20 can be increased by connecting a capacitor 21 inparallel with the battery 1. Since the power that can be supplied fromthe capacitor 21 to the load 20 is proportional to the capacitance, acapacitor 21 with extremely high capacitance, for example, 4000 μF to6000 μF, is used. When a high capacitance capacitor 21 in the dischargedstate is connected to a battery 1 with high output voltage, extremelyhigh transient charging current will flow. This is because capacitor 21impedance is very low.

The battery 1 activates the electric motor 22 that drives the car. Tosupply high power to the motor 22, battery 1 output voltage is increasedby connecting many rechargeable batteries 10 in series. Nickel hydridebatteries or lithium ion rechargeable batteries are used as therechargeable batteries 10. However, any batteries that can be recharged,such as nickel cadmium batteries, can be used as the rechargeablebatteries 10. To supply high power to the motor 22, battery output isincreased to a high voltage, for example, 300V to 400V. However, battery1 output voltage for the power source apparatus can be also increased byconnecting a DC/DC converter to the output-side of the battery 1 (notillustrated). In this type of power source apparatus, the number ofrechargeable batteries connected in series can be reduced and battery 1output voltage can be lowered. For example, battery 1 output voltage canbe 150V to 400V.

The pre-charge circuit 3 pre-charges the capacitor 21 while limitingcurrent. This pre-charge circuit 3 has a pre-charge resistor 6 andpre-charge relay 7 connected in series. The pre-charge resistor 6 isconnected in parallel with the first contactor 2A, and the pre-chargerelay 7 is connected in series with the first contactor 2A.Consequently, the positive-side of the battery 1 connects to thecar-side via a series connection of the first contactor 2A and thepre-charge relay 7. Therefore, the positive-side of the battery 1 can becut-off from the car-side by switching OFF either the first contactor 2Aor the pre-charge relay 7.

In this power source apparatus, when the ignition switch (notillustrated) is turned ON, the second contactor 2B is switched ON.Subsequently, the first contactor 2A is maintained in the OFF statewhile the pre-charge relay 7 is switched ON to pre-charge the capacitor.After the capacitor is pre-charged, the control circuit maintains thesecond contactor 2B and the pre-charge relay 7 ON and switches the firstcontactor 2A ON. When the ignition switch is turned OFF, the firstcontactor 2A, which is connected in series with the pre-charge relay 7,is switched OFF. Subsequently, the second contactor 2B and thepre-charge relay 7 are switched OFF to cut-off battery 1 output at thepositive and negative-sides.

The pre-charge resistor 6 limits pre-charge current to the load 20capacitor 21. Pre-charge circuit 3 pre-charge current can be reduced byincreasing the electrical resistance value of the pre-charge resistor 6.For example, in a power source apparatus with 400V of battery 1 outputvoltage and a 1Ω pre-charge resistor, the maximum value of thepre-charge current is 40A. The maximum value of the pre-charge currentcan be reduced by increasing the resistance of the pre-charge resistor6. However, the time to pre-charge the capacitor 21 becomes longer asthe resistance of the pre-charge resistor 7 is increased. This isbecause the pre-charge current decreases. The resistance of thepre-charge resistor 6 is set considering the pre-charge current and thetime for pre-charging, and is, for example 5Ω to 20Ω, preferably 6Ω to18Ω, and more preferably 6Ω to 15Ω.

The pre-charge resistor 6 of the pre-charge circuit 3 is connected inparallel with the first contactor 2A. The first contactor 2A isconnected on the positive-side of the battery 1, the second contactor 2Bis connected on the negative-side, and the pre-charge circuit 3 isconnected on the positive-side. The capacitor 21 is pre-charged by thepre-charge circuit 3 with the second contactor 2B, which is connected tothe negative-side of the battery 1, in the ON state. For the prior artpower source apparatus of FIG. 1, after the capacitor 21 is pre-chargedby the pre-charge circuit 3, the positive-side contactor 2A is switchedON and the pre-charge circuit 3 pre-charge relay 7 is switched OFF.

The control circuit 4 for the power source apparatus of FIG. 2 controlsthe first contactor 2A, the second contactor 2B, and the pre-chargerelay 7 with signals input from the ignition switch (not illustrated),which is the main switch on the car-side. For an ON signal from theignition switch, the control circuit 4 maintains the first contactor 2Ain the OFF state, and switches the second contactor 2B and thepre-charge relay 7 ON to pre-charge the capacitor 21. After thecapacitor has been pre-charged, the pre-charge relay 7 is maintained inthe ON state and the first contactor 2A is switched ON to connect thepositive-side and the negative-side of the battery 1 to the car-side.

The first contactor 2A, the second contactor 2B, and the pre-chargerelay 7 are relays having mechanically moveable contacts. FIG. 4 showsan abbreviated diagram of a relay for the first contactor, and FIG. 5shows an abbreviated diagram of a relay for the pre-charge relay and thesecond contactor. In the relays shown in these figures, the controlcircuit 4 controls current in the magnetic coil 5, 8 to switch thecontacts ON and OFF. A relay has a plunger that is pulled in by currentflow through the magnetic coil 5, 8, and moveable contacts 11, 12 areattached to that plunger. Fixed contacts 13, 14 are disposed oppositethe moveable contacts 11, 12. When current flows through the magneticcoil 5, 8, the plunger is pulled into the coil to put the moveablecontacts 11, 12 in contact with the fixed contacts 13, 14 and turn therelay ON. When current through the magnetic coil is cut-off, the plungerreturns to its initial position via a spring, the moveable contacts 11,12 separate from the fixed contacts 13, 14, and the relay is switchedOFF.

The relay of FIG. 4 (used for the first contactor 2A) is provided withhigh durability, longer-lifetime contacts 11 than those of thepre-charge relay 7. This is to achieve sufficient durability forrepeated ON-OFF switching. The relay of FIG. 4 is provided with highdurability contacts 11 with tungsten surfaces. Tungsten has a highermelting point and longer-lifetime compared to metals such as copper. Inthe relay of FIG. 4, tungsten is layered on the surface of copper tomake highly durable contacts 11. In this relay, fixed contacts 13 arecopper, and moveable contacts 11 have a tungsten surface. The moveablecontacts 11 have tungsten layered on the surface of copper for highdurability. Although not illustrated, the relay for the first contactor2A can also have high durability contacts with moveable contacts thatare copper and fixed contacts that have tungsten layered on the surfaceof copper. Although contacts with a tungsten surface have superiordurability compared to copper contacts, the present invention does notlimit the material for high durability contacts to tungsten. Contactsfor the first contactor 2A can use any metal that results in contactsthat are more durable than those of the pre-charge relay 7. For example,tungsten alloys and other metals can be used, and high durabilitycontacts can be solid single-metal contacts rather than a layeredstructure of different metals.

FIG. 5 shows a relay used as the second contactor 2B and the pre-chargerelay 7, and it is provided with contacts 12, 14 that are highercapacity than those of the first contactor 2A. The relay of the figurehas fixed contacts 14 and moveable contacts 12 that are copper. Thefixed contacts 14 and moveable contacts 12 can also be high capacitytype contacts made of a copper alloy rather than pure copper. Comparedto high durability contacts such as tungsten, copper contacts, which arehigh capacity type contacts, have smaller electrical resistance, largerspecific heat, and generate less heat due to short circuit current. Forexample, compared to a 900° C. contact temperature due to short circuitcurrent for copper contacts, high durability tungsten contacts wouldreach approximately 1500° C. Since the melting point of copper is 1000°C., copper contacts would fuse together if heated to 1500° C. For highcapacity type copper contacts as fixed contacts and moveable contacts,even if heated to 900° C. by short circuit current, the contacts willnot fuse together. This is because 900° C. is below the melting point ofcopper. However, these copper contacts will not be high durability,long-lifetime contacts.

To extend the lifetime of high capacity type contacts in the pre-chargerelay 7 and second contactor 2B, the control circuit 4 switches OFF thesecond contactor 2B and the pre-charge relay 7 after cutting-off battery1 current with the first contactor 2A. Therefore, the control circuit 4controls the first contactor 2A, the second contactor 2B, and thepre-charge relay 7 ON and OFF according to the following operation.

The control circuit 4 pre-charges the car-side capacitor 21 when anignition switch ON signal is detected. The control circuit 4 switchesthe second contactor 2B and the pre-charge relay 7 ON with the firstcontactor 2A in the OFF state to pre-charge the capacitor. In thisstate, capacitor pre-charge current is limited by the pre-chargeresistor 6. The control circuit 4 detects completion of capacitorpre-charge from the time passed since pre-charge was started, thecar-side voltage, and the pre-charge current. Since pre-charge iscomplete when a given time has elapsed after the start of pre-charge,pre-charge completion can be detected from elapsed time. In addition,since the voltage across the capacitor increases and pre-charge currentdecreases as the capacitor becomes pre-charged, pre-charge completioncan be detected from the car-side voltage or pre-charge current. Afterthe control circuit 4 detects completion of pre-charge, it maintains thesecond contactor 2B and the pre-charge relay 7 ON and switches ON thefirst contactor 2A, which was in the OFF state. In this state, power issupplied from the battery 1 to the car-side.

When the control circuit 4 detects an ignition switch OFF signal, itmaintains the second contactor 2B and the pre-charge relay 7 in the ONstate and switches the first contactor 2A OFF. Subsequently, the controlcircuit 4 switches the pre-charge relay 7 and the second contactor 2BOFF.

[Possible Use in the Industry]

The power source apparatus of the present invention is installed in avehicle to supply power to the electric motor that drives the vehicle.

It should be apparent to those with an ordinary skill in the art thatwhile various preferred embodiments of the invention have been shown anddescribed, it is contemplated that the invention is not limited to theparticular embodiments disclosed, which are deemed to be merelyillustrative of the inventive concepts and should not be interpreted aslimiting the scope of the invention, and which are suitable for allmodifications and changes falling within the spirit and scope of theinvention as defined in the appended claims. The present application isbased on Application No. 2008-40716 filed in Japan on Feb. 21, 2008, thecontent of which is incorporated herein by reference.

1. A car power source apparatus comprising: a battery; contactorsconnected to the output-side of the battery; a capacitor connected tothe car-side of the battery; a pre-charge circuit connected to acontactor and made up of a series connection of pre-charge resistor andpre-charge relay to provide auxiliary charge to the capacitor; and acontrol circuit to control the contactors and pre-charge relay; whereinthe pre-charge resistor is connected in parallel with a contactor, thepre-charge relay and that contactor are connected in series; and thecontrol circuit switches the pre-charge relay ON to pre-charge thecar-side capacitor, and switches the contactor ON to connect the battery1 to the car-side.
 2. A car power source apparatus as cited in claim 1wherein the contactors are provided with a first contactor and a secondcontactor connected to the positive and negative output-side of thebattery; the pre-charge resistor is connected in parallel with the firstcontactor, and the first contactor and the pre-charge relay areconnected in series.
 3. A car power source apparatus as cited in claim 2wherein the first contactor is connected to the positive-side of thebattery and the second contactor is connected to the negative-side ofthe battery.
 4. A car power source apparatus as cited in claim 1 whereinthe pre-charge circuit and a contactor are connected only to thepositive-side of the battery.
 5. A car power source apparatus as citedin claim 1 wherein the battery has many rechargeable batteries connectedin series and the rechargeable batteries are lithium ion batteries.
 6. Acar power source apparatus as cited in claim 1 wherein the battery hasmany rechargeable batteries connected in series and the rechargeablebatteries are nickel hydride batteries.
 7. A car power source apparatusas cited in claim 1 wherein the electrical resistance of the pre-chargeresistor is from 5Ω to 20Ω.
 8. A car power source apparatus as cited inclaim 1 wherein the contactor connected in series with the pre-chargerelay is provided with contacts that are highly durable andlonger-lifetime than those of the pre-charge relay.
 9. A car powersource apparatus as cited in claim 1 wherein the contacts of thepre-charge relay are a higher capacity type than those of the contactorconnected in series with the pre-charge relay.
 10. A car power sourceapparatus as cited in claim 1 wherein the contacts of the contactorconnected in series with the pre-charge relay are highly durable,long-lifetime contacts having tungsten at least on the surface.
 11. Acar power source apparatus as cited in claim 10 wherein the contacts ofthe contactor connected in series with the pre-charge relay are highlydurable, long-lifetime contacts having tungsten layered on a coppersurface.
 12. A car power source apparatus as cited in claim 10 whereinthe contacts of the contactor connected in series with the pre-chargerelay are highly durable, long-lifetime contacts with copper contacts onone side and tungsten on the surface of the contacts on the other side,which mates with the copper contacts.
 13. A car power source apparatusas cited in claim 10 wherein the contacts of the contactor connected inseries with the pre-charge relay are highly durable, long-lifetimecontacts with fixed contacts of copper and moveable contacts, which matewith the fixed contacts, having tungsten on the surface.
 14. A car powersource apparatus as cited in claim 10 wherein the contacts of thecontactor connected in series with the pre-charge relay are highlydurable, long-lifetime contacts with fixed contacts of copper andmoveable contacts, which mate with the fixed contacts, made of an alloyof tungsten.
 15. A car power source apparatus as cited in claim 10wherein the contacts of the first contactor connected in series with thepre-charge relay have a layered structure of different kinds of metals.16. A car power source apparatus as cited in claim 1 wherein thecontacts of the pre-charge relay are high capacity type contacts made ofcopper.
 17. A car power source apparatus as cited in claim 2 wherein thecontacts of the second contactor are higher capacity type contactscompared to those of the first contactor.
 18. A car power sourceapparatus as cited in claim 17 wherein the contacts of the secondcontactor are high capacity type contacts made of copper.
 19. A carpower source apparatus as cited in claim 17 wherein the contacts of thesecond contactor are high capacity type contacts made of an alloy ofcopper.
 20. A car power source apparatus as cited in claim 1 wherein thecontrol circuit stores in memory the delay time to switch the pre-chargerelay OFF after switching OFF the contactor connected in series with thepre-charge relay; and the control circuit detects the time elapsed afterswitching OFF the contactor connected in series with the pre-chargerelay to switch OFF the pre-charge relay.